Hot beverages such as cappuccino are becoming increasingly popular. Such beverages are often given a topping of foamed milk. When hot beverages are sold by commercial businesses such as fast food restaurants, such a topping may often be made from powder products. However, many customers prefer a topping made from real milk. Therefore, there is a need for devices that can use real milk and transform the milk to milk foam and such devices are also used worldwide. A solution which has been used in many such devices is to add hot steam to the milk in order to transform the milk to foam. U.S. Pat. No. 7,258,062 discloses a system and a method for producing foamed and steamed milk by means of pressurized air and steam. Pressurized air is added to pressurized milk and steam is supplied from a steam generator. The steam may be pressurized. From a mixing area, a mixture of milk, air and steam is passed through an expansion area where expansion may cause the milk, air and steam mixture to foam as pressure is reduced. In such a system, it is difficult to control the temperature of the milk. Moreover, the function is dependent on the supply of steam. A different method is disclosed in U.S. Pat. No. 7,527,818. The method disclosed in that patent includes suctioning milk from a container into a suction line by means of a pump. The milk is conveyed through a continuous-flow heater which is disposed in the suction line. Air is added to the milk before the milk passes through the continuous flow heater such that the milk that passes through the heater is mixed with air. Downstream of the pump, a there is a throttle point with an adjustable throttle valve. The pressure can be adjusted by means of the throttle valve. It is stated that the temperature of the heater element is controllable for the purpose of adjusting the temperature of the milk/air mixture at the outlet of the continuous-flow heater.
It is a purpose of the present invention to provide an improved method and an improved system for producing foamed milk for hot beverages such as coffee or chocolate. One purpose of the invention is to provide an effective way of transforming the milk into foam. Another purpose is to provide an effective and reliable way of heating the milk. Yet another purpose is to provide an effective way of cleaning the system after a quantity of milk has been passed through the system.